Insulated storage tank with insulation restrained against settling because of metal contraction

ABSTRACT

Disclosed is an improved insulated tank having a part thereof which is double walled. The double-walled portion, which may be cylindrical, spherical or some other shape, contains free-flowing insulating material and a resilient insulating blanket which has been compressed by active pressure substantially above the lateral passive pressure caused by the free-flowing, usually granular, insulation. When the inner wall of the tank contracts during low-temperature use, such as in the storage of a cryogenic liquid, the blanket expands sufficiently far and with enough pressure to occupy the increased insulating space without settling of the free-flowing insulation.

United States Patent [72] Inventor Kenneth Wilson Lange 3,147,878 9/1964 Wissmiller 220/l5X Hinsdale. Ill. 3.273.740 9/1966 Herrenschmidt 220/15 i211 Appl N0 315,531 1968 FOREIGN PATENTS [22] Fi e u y 7 [45] v Patented Feb'z, 197 234.484 7/1961 Australia 20/9(A1) [73] Assignee Chicago Bridge & Iron Company Primary Examiner-David Ml Bockenek Oak Brook, Ill. Assistant Examiner-J ames R, Garrett a corporation of Illinois Attorney-Merriam. Marshal, Shapiro & Klose [54] INSULATED STORAGE TANK WITH INSULATION RESTRAINED AGAINST SETTLING BECUASE OF METAL CONTRACTION ABSTRACT: Disclosed is an improved insulated tank having a 11 Claims Drawing Figs part thereof which is double walled, The double-walled portion. which may be cylindrical, spherical or some other shape, U.s. contains free fl0wlng insulating material and a resilient insul5 l] Il Cl B65d 7/22 lating blanket which has been compressed by active pressure [50] Field of Search 220/9A. Substantially above the lateral passive pressure caused by the 9A] f l0 15' l 14/74A1 (l2/45 free-flowing, usually granular, insulation. When the inner wall of the tank contracts during low-temperature use, such as in [56] References Cited the storage of a cryogenic liquid, the blanket expands suf- UNITED STATES PATENTS ciently far and with enough pressure to occupy the increased 3,1 18,194 l/ 1964 Biais i. 220/9X insulating space without settling of the free-flowing insulation.

I 5 1)/ 2 2 2.5 f x 5 l 2 .i I s., 342 egg (if, c t' Jj t s 26 2 7 23 fg u' l l '2 f i iig y? r l l l .s Z8 "Hfs: :l1- bh 2g I, .7g/i j f 717 '(e i 'il' 2y l .y l 7 o HD1;

,il 55? n i 3 m 3*? y," 30 19 iz/ 20 if ".v n W l "0.;1 `".,\l".r 04W eww/w/,Y/Q/M/svmw/myw/ INSULATED STORAGE TANK WITH INSULATION RESTRAINED AGAINST SETTLING BECUASE OF METAL CONTRACTION This invention relates to tanks and vessels used for the storage of liquids and gases. More particularly, it is concerned with such tanks which are insulated in order for them to function satisfactorily during use of the tank for low-temperature storage.

Tanks and vessels are widely used for storing liquids and gases. Many such uses require that the tank or vessel be insulated either to keep heat out or to keep heat in. Insulation is used to retard heat flow into a tank or vessel used for storing liquiiied gases such as liquitied nitrogen. oxygen, helium, ethylene or methane.

One way of insulating has been to produce tanks or vessels having at least part thereof in the form of a double-walled structure and to place a free-flowing, usually granular, insulating material therein. This approach is satisfactory in tanks which are not cycled through wide temperature ranges. However, in tanks which go through a wide temperature range, such as from the construction temperature to a low-tempera ture in use for storing liquifred oxygen, methane and other normally gaseous products, and back to ambient temperature when empty, a substantial shrinkage or contraction of the inner wall takes place with enlargement of the annular space between the inner and outer walls of the tank. The free-flowing insulation settles downwardly to occupy the space developed by contraction of the inner wall. This results in a settling or dropping of the 'free-flowing insulating material to such an extent that the upper part of the tank becomes devoid of the necessary insulation and thereby provides a ready route for heat transfer into the tank.

Wissmiller U.S. Pat. No. 3,147,878 provides a structure designed to overcome the described shortcomings in insulated tanks using free-flowing granular or loose insulation between double-walled structures. Wissmiller proposed to overcome settling of the free-flowing insulation by placing a resilient insulating blanket or mattress in the space between the walls of the tank or vessel. As the inner wall of the tank contracted as it became colder, such as during filling with a cryogenic liquid, like liquified oxygen or liquied methane, the increased space or volume between the two walls of the tank was to be filled through lateral expansion of the resilient insulating blanket. The system described in the Wissmiller patent has found substantial commercial use and thus is suitable for many tank structures. However, in the Wissmiller system there would be only a slight amount of compression of the blanket because of the active pressure on it from the loose granular insulation as it is placed in the double-wall space. The compression of the blanket because of this effect is slight and as the inner wall contracts upon cooling, expansion of the flexible blanket to its normal size is effectively prevented by continuing active pressure exerted by the granular insulation. As a result of the combination of these effects the granular insulation in the doublewall space settles. When the inner tank again expands the passive pressure which the granular material is capable of taking, being much higher than the active pressure, effectively prevents any reversal of the flow of the granular insulation material that would return it to its original state. This permits the granular insulation between the walls or shells to settle and develop areas devoid of insulation. As a result, there is a need for an improved insulated tank which will maintain free-flowing insulation in place in vertical or sloped double-walled sides, such as in cylindrical or spherical tanks, through all ranges of temperature to which the tank is subjected during initial cooling and use and which will maintain the free-flowing insulation in place against significant settling to thereby avoid any subsequent need to resupply free-flowing insulation thereto.

According to the present invention there is provided an improved insulated tank or vessel for storing liquids and gases. The invention broadly comprises the use of a compressed or squeezed resilient insulating blanket or mattress together with free-flowing, i.e. granular or loose, insulating material in the space formed by those portions of the tank or vessel which have an inner and an outer wall. Subjecting the insulating blanket to an applied force, thereby compressing it, permits it to expand laterally for a greater distance and at a higher pressure than would be possible by subjecting the insulating blanket only to the passive pressure exerted against the blanket solely by the free-flowing insulation placed between the inner and outer walls of the tank. As a result, contraction of the inner wall or shell of the insulated tank, which leads to an increase in the space or volume between the inner and outer walls, is readily and continuously adjusted to by lateral expansion of the compressed insulating blanket. The increased cornpression of the blanket, beyond that normally applied laterally against it by the free-flowing insulation, causes it to expand with sufficient lateral force to prevent the free-flowing insulation from settling and to maintain it at the same level between the inner and outer walls. It thus becomes unnecessary subsequently to resupply said insulating space with free-flowing insulation.

Although the invention has applicability to a wide variety of insulated tanks and vessels, including spherical vessels, its greatest usefulness is presently considered to be in cylindrical tanks having an insulated bottom, a vertical side and a top or roof which is supported by the side. It is in conjunction with such structures that the invention will be described in greatest detail and which are illustrated specifically in the attached drawings.

The invention will now be described in conjunction with the attached drawings, in which:

FIG. l is a vertical sectional view through an insulated tank showing one embodiment of the invention in which compresf sion of the insulating blanket is effected by evacuating a space around the blanket and letting external pressure compress the blanket;

FIG. 2 is a partial sectional view of the wall structure of the tank of FIG. 1 and illustrates the contraction of the inner wall;

FIG. 3 is a vertical sectional view of an insulated tank showing a winding around the insulating blanket to compress the same;

FIG. 4 is a partial sectional view of an insulated tank showing a continuous membrane circumscribing the insulating blanket to compress the same;

FIG. 5 is an isometric view of a wall structure of an insulated tank showing an overlapped band or strip around the insulating blanket to compress the same; and

FIG. 6 is an isometricview in section of an insulated tank structure showing a meshwork or screen structure surrounding the insulating blanket to compress the same.

So far as in practical identical elements which appear in the FIGS. of the drawings will be identified by the same number. It should be understood, however, that the drawings are merely illustrative of the invention and it is not the intent of the inventor to restrict the scope of his invention to the embodiments thereof set forth in the drawings.

With reference to FIGS. l and 2, the insulated tank 10 has a bottom l1, side 12 and top 13. The bottom comprises a metal plate 14 resting on a suitable foundation. Plate 14 supports load bearing insulation l5 which in turn supports the inner floor 16. The tank side 12 has an inner metal wall 17 and an outer metal wall 18. The inner metal wall is joined at the floor edge to plate 16 by weld 19. Similarly, outer metal wall 18 is welded at 20 to plate 14. The top of the tank has single plate noninsulated metal roof 2l, which is generally dome-shaped, and which can rest on inner wall 17 and/or the outer wall 18 but which, as shown in FIG. 1, rests primarily on inner wall 17 with an extension 22 joining the outer wall 18. Plate 22 serves to seal off annular insulating space 23 between the inner and outer walls 17 and l8.`

Roof shell 21 is reinforced by ribs 24 welded to the lower side thereof and from which struts 25 extend downwardly to support plate 26 on which insulation 27 rests, thereby providing an insulated suspended ceiling inside of the tank. Of

course. other types of insulated ceilings or roofs can be used sincc the invention is not restricted to any particular top structurc.

Positioned in annular insulating space 23 is insulating blanket 28. Flexible gas impervious membrane 29 is joined at its lower edge by suitable means, such as bolts 30, to plate I6 and at its upper edge 31 to inner wall 17. Membrane 29 extends completely around the outer face of insulating blanket 28. As a result. the insulating blanket is enclosed in an evacuable space. This space can be reduced in pressure by means of pipe 32 which communicates therewith and connects to vacuum pump 33. Valved vent 34 communicates with annular space 23 and permits air to enter and leave such space. By drawing a vacuum by means of pipe 32, the pressure in the space occu pied by blanket 28 is reduced to such an extent that atmospheric pressure maintained on the outside of membrane 29, by having valved vent 34 open, causes the insulating blanket 28 to be laterally compressed. While in such compressed state, granular insulation 34 can be placed in annular space 23 to a height adequate to completely insulate the side 12 at least up to the insulating ceiling. Of course, granular insulation 35 can be put in place before the vacuum is created by means of pipe 32. Creating the vacuum will result in compression of insulating blanket 28 and lead to settling of the granular material 35. Sufficient additional granular insulation can be supplied to bring the top surface up to the desired level. Once the granular insulation is in place, and the insulating blanket has been compressed, there is no longer any necessity to maintain a vacuum between inner wall 17 and membrane 29. This is because the compressed state of the blanket will be maintained by the walls and the granular insulation.

An alternative method of compressing the insulating blanket in FIG. 1 is to supply pressurized gas such as air by means of valve 34 into space 23. This will cause the blanket to be compressed, particularly if air between membrane 29 and wall 17 is vented out such as by means of pipe 32, with or without the aid of pump 33. Granular material 35 can be placed in annular space 23 to partially fill the same before the pressure is applied and the remainder of the granular material added while maintaining the pressureA Of course, all the granular material can be added after the pressure is created and while it is maintained.

Some of the free-flowing granular or loose insulating materials which can be suitably used are expanded perlite, expanded vermiculite, silica aerogel and granulated wood.

Some of the types of insulating blankets which can be used are described in detail in Wissmiller U.S. Pat. No. 3,147,878. However, of particular use is a fiberglass blanket. It is to be understood that choice of materials for use in the invention is to be made in light of engineering experience, availability, cost safety requirements and other factors normally involved in this art with the object always to produce a useful and acceptable structure.

As shown in FIG. 2, inner wall 17 can contract substantially, such as in the area 40, thereby increasing the space or volume to be occupied by the insulating blanket. Since insulating blanket 28 is under a compressive force substantially greater than that attributable solely to the passive pressure that the granular insulation 3S is capable of sustaining, it can quite readily expand to occupy the increased volume while maintaining a sufficient pressure against the granular insulation to prevent its settling.

The tank structure shown in FIG. 3 is very similar in most structural elements to that of FIGS. l and 2 and accordingly the same identifying numbers have been used where appropriate. The main structural difference is that in FIG. 3 the insulating blanket 28, which is in contact with inner wall 17, has been compressed by a winding in tension. The winding comprises band 40 which starts at the bottom edge of the insulating blanket 28 and while in tension, winds helically around and around the insulating blanket and compresses the insulating blanket 28 to the extent desired. Band 40 can be made of any suitable material and can be metallic or nonmetallic. lf

metallic it should, however, not have a thermal contraction coefficient nearly as great as that of inner wall 17,

The structure of FIG. 3 does not require use of a vacuum to compress insulating blanket 28. The nature of the structure however makes it advisable to generally completely wrap the band around the insulating blanket before granular insulation 35 is put in place. Once granular insulation 35 is in place, tension on band 40 can be released since release at such time does not alter the amount of compression on the insulating blanket 28. Also` release of tension in the restraining band will not substantially change the pressure on the insulating blanket because of the relatively high passive pressure that the granular material is capable of sustaining. Also shown in FIG. 3, in a schematic form` is inner wall 17 as it might contract to position 17A upon cooling to a low temperature encountered during storage of a cryogenic liquid such as liquified methane. Space 45, comprising the increased volume resulting from displacement of the inner wall from its normal position 17 to its contracted state 17A is occupied through expansion of the compressed insulating blanket 28 without settling of granular insulation 35.

Instead of a single band helically wound around the blanket a plurality of circumferential hoops or rings spaced apart from each other can be wrapped around the blanket to compress it.

The structure of FIG. 4 is similar to that of FIG. 3 except that a continuous membrane 50 is placed around insulating blanket 28 to effect the desired compression. Membrane 50 is placed in sufficient tension so that the compression is obtained. Any suitable material whether metallic or nonmetallic which can withstand the low temperature operating conditions can be used for this purpose providing it does not contract significantly upon cooling. Sheets of nylon, polychlorotrifluoroethylene and polyethylene terephthalate and woven fabrics of fiberglass, cotton and nylon are typical materials which can be used for the membrane. Tension on the membrane can be released, if desired, after the granular insulation is in place.

The wall structure of FIG. 5 is essentially like that shown in l the previous FIGS. of the drawings except that insulating blanket 28 is placed in compression by wide strips 60 which are wrapped in tension in an overlapping condition around the outside of insulating blanket 28. Thus, the result is quite similar to that described in conjunction with FIG. 3 except that where in FIG. 3 the bands are spaced apart, the strips or bands 60 as shown in FIG. 5 are placed in an overlapping arrangement.

FIG. 6 also shows a walled structure in which the insulating blanket 28 is placed in compression although in this form the screen or meshwork 70 is placed in tension around the outside surface of insulating blanket 28 to achieve its compression. The screen can be metallic or nonmetallic.

Iclaim:

1. An enclosed insulated tank or storing liquids or gases at low temperatures, at least part of said tank having a substantially vertical inner metal wall portion surrounded by a substantially vertical outer metal wall portion spaced apart from the inner wall portion thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycles of said tank, a substantially vertically extending resilient insulating blanket portion positioned in the insulating space, and free-flowing insulation filling the remainder of the insulating space, said resilient blanket being compressed horizontally to an extent substantially greater than the horizontal pressure applied to the blanket'by the frecflowing insulation and restricted to a constant maximum size with suicient horizontal force to prevent settling of the freeflowing insulation by expansion of the blanket with increase in volume between the inner and outer walls upon contraction of the inner wall and to continuously maintain the granular insulation at the same level between the inner and outer walls.

2. A tank according to claim l having means compressing the blanket against the inner metal wall.

3. An enclosed tank having an insulated bottom, vertical sidewalls and a top supported by the sidewalls, the sidewalls comprising an inner metal wall surrounded by an outer metal wall spaced apart from the inner wall thereby defining an insulating space. said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycle of said tank, a resilient insulating blanket positioned vertically in the insulating space, and free-flowing insulation fillingvthe remainder of the insulating space, said resilient blanket being horizontally compressed to an extent substantially greater than the horizontal pressure applied to the blanket by the free-flowing insulation and restricted to a constant maximum size with sufficient horizon tal force to prevent settling of the free-flowing insulation by expansion of the blanket with increase in volume between the inner and outer walls upon contraction of the inner wall and to continuously maintain the granular insulation at the same level between the inner and outer walls.

4. A tank according to claim 3 having means compressing the blanket against the inner metal wall and restricting same to a constant maximum size.

5. A tank according to claim 4 in which a substantially nonextensible screen or meshwork in tension surrounds and compresses the blanket against the inner wall.

6. A tank according to claim 4 in which a plurality of substantially nonextensible bands under tension surround and compress the blanket against the inner wall.

7. A tank according to claim 4 in which a substantially nonextensible winding under tension surrounds and compresses the blanket against the inner wall.

8. A tank according to claim 7 in which the winding is a strip with adjacent edges spaced apart from each other.

9. A tank according to claim 7 in which the winding is a strip with adjacent overlapping edges.

l0. An enclosed insulated tank for storing liquids or gases at low temperatures, at least part of said tank having a substantially vertical inner metal wall portion surrounded by a substantially vertical outer metal wall portion spaced apart from the inner wall portion thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycle of said tank, a resilient insulating blanket substantially vertically positioned in the insulating space, freeflowing insulation filling the remainder of the insulating space, and a flexible nonmetallic substantially nonextensible gas-impervious membrane between the blanket and the free-flowing insulation, said membrane forming an evacuable space between the membrane and the inner wall and restricting the outer surface of said blanket to a substantially constant maximum size, said resilient blanket being horizontally compressed by the membrane to an extent substantially greater than the horizontal pressure applied to the blanket by the freef`lowing insulation.

l1. An enclosed tank having an insulated bottom, vertical sidewalls and a top supported by the sidewalls, the sidewalls comprising an inner metal wall surrounded by an outer metal wall spaced apart from the inner wall thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycle of said tank, a resilient insulating blanket positioned vertically in the insulating space, and free-flowing insulation filling the remainder of the insulating space, and a flexible nonmetallic gas-impervious substantially nonextensible membrane between the blanket and the freeflowing insulation, said membrane forming an evacuable space between the membrane and the inner wall and restricting the outer surface of said blanket to a substantially constant maximum size, said resilient blanket being horizontally compressed by the membrane to an extent substantially greater than the horizontal pressure applied to the blanket by the freeflowing insulation. 

1. An enclosed insulated tank or storing liquids or gases at low temperatures, at least part of said tank having a substantially vertical inner metal wall portion surrounded by a substantially vertical outer metal wall portion spaced apart from the inner wall portion thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycles of said tank, a substantially vertically extending resilient insulating blanket portion positioned in the insulating space, and free-flowing insulation filling the remainder of the insulating space, said resilient blanket being compressed horizontally to an extent substantially greater than the horizontal pressure applied to the blanket by the freeflowing insulation and restricted to a constant maximum size with sufficient horizontal force to prevent settling of the freeflowing insulation by expansion of the blanket with increase in volume between the inner and outer walls upon contraction of the inner wall and to continuously maintain the granular insulation at the same level between the inner and outer walls.
 2. A tank according to claim 1 having means compressing the blanket against the inner metal wall.
 3. An enclosed tank having an insulated bottom, vertical sidewalls and a top supported by the sidewalls, the sidewalls comprising an inner metal wall surrounded by an outer metal wall spaced apart from the inner wall thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycle of said tank, a resilient insulating blanket positioned vertically in the insulating space, and free-flowing insulation filling the remainder of the insulating space, said resilient blanket being horizontally compressed to an extent substantially greater than the horizontal pressure applied to the blanket by the free-flowing insulation and restricted to a constant maximum size with sufficient horizontal force to prevent settling of the free-flowing insulation by expansion of the blanket with increase in volume between the inner and outer walls upon contraction of the inner wall and to continuously maintain the granular insulation at the same level between the inner and outer walls.
 4. A tank according to claim 3 having means compressing the blanket against the inner metal wall and restricting same to a constant maximum size.
 5. A tank according to claim 4 in which a substantially nonextensible screen or meshwork in tension surrounds and compresses the blanket against the inner wall.
 6. A tank according to claim 4 in which a plurality of substantially nonextensible bands under tension surround and compress the blanket against the inner wall.
 7. A tank according to claim 4 in which a substantially nonextensible winding under tension surrounds and compresses the blanket against the inner walL.
 8. A tank according to claim 7 in which the winding is a strip with adjacent edges spaced apart from each other.
 9. A tank according to claim 7 in which the winding is a strip with adjacent overlapping edges.
 10. An enclosed insulated tank for storing liquids or gases at low temperatures, at least part of said tank having a substantially vertical inner metal wall portion surrounded by a substantially vertical outer metal wall portion spaced apart from the inner wall portion thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycle of said tank, a resilient insulating blanket substantially vertically positioned in the insulating space, free-flowing insulation filling the remainder of the insulating space, and a flexible nonmetallic substantially nonextensible gas-impervious membrane between the blanket and the free-flowing insulation, said membrane forming an evacuable space between the membrane and the inner wall and restricting the outer surface of said blanket to a substantially constant maximum size, said resilient blanket being horizontally compressed by the membrane to an extent substantially greater than the horizontal pressure applied to the blanket by the free-flowing insulation.
 11. An enclosed tank having an insulated bottom, vertical sidewalls and a top supported by the sidewalls, the sidewalls comprising an inner metal wall surrounded by an outer metal wall spaced apart from the inner wall thereby defining an insulating space, said insulating space being subject to substantial changes in horizontal width caused by thermally-induced expansions and contractions produced in said inner wall during the loading and emptying cycle of said tank, a resilient insulating blanket positioned vertically in the insulating space, and free-flowing insulation filling the remainder of the insulating space, and a flexible nonmetallic gas-impervious substantially nonextensible membrane between the blanket and the free-flowing insulation, said membrane forming an evacuable space between the membrane and the inner wall and restricting the outer surface of said blanket to a substantially constant maximum size, said resilient blanket being horizontally compressed by the membrane to an extent substantially greater than the horizontal pressure applied to the blanket by the free-flowing insulation. 